The present invention relates generally to compositions comprising hydrofluorocarbons and water. More specifically, the present invention provides compositions comprising pentafluoropropane, pentafluorobutane and water for use in a wide variety of applications including as blowing agents, refrigerants, propellants, solvents, and the like.
Hydrofluorocarbons (xe2x80x9cHFCsxe2x80x9d) and HFC-based compositions are of interest for use in replacing environmentally undesirable chlorofluorocarbons (xe2x80x9cCFCsxe2x80x9d) and hydrofluorocarbons (xe2x80x9cHCFCsxe2x80x9d) in a wide range of applications. Applicants have recognized, for example, that many HFC-based compositions are particularly well-suited for use as blowing agents in methods for making rigid foams.
As is known in the art, many rigid foams, including rigid polyurethane and isocyanate foams, are produced by reacting polymerizing reagents in the presence of a blowing agent composition. See, for example, Saunders and Frisch, Volumes I and II Polyurethanes Chemistry and Technology (1962), which is incorporated herein by reference. In general, as the polymerization reagents are reacted, the blowing agent either reacts with one or more of the polymerizing agents, or preferably, is vaporized by the exotherm of the reaction mixture, to form a gas. This gas is then encapsulated by the reaction mixture polymer to create cells which expand the polymer mixture. After expanding, the polymer mixture is cured to form a rigid closed-cell foam.
Applicants have come to appreciate that HFCs, like many other fluorocarbons, tend to be both highly volatile and relatively inert under conventional foam-producing conditions. Accordingly, under such conditions, HFCs tend to vaporize to form HFC vapor which can be encapsulated by a wide variety of polymer mixtures to form rigid foams. The foams produced using such HFC-based blowing agents tend to exhibit desirable thermal characteristics and, thus, applicants have identified HFCs as potential replacement blowing agents of interest.
Applicants have further recognized that certain benefits may be realized by using blowing agent compositions comprising not only HFCs, but also water. Under conventional foam-forming conditions, water tends to react with certain polymerization reactants to form carbon dioxide which can be encapsulated by polymerization reaction mixture to form cells. Accordingly, water contributes to the formation of cells in foams and is suitable for use in blowing agents. Moreover, because water is highly environmentally desirable and has very little cost associated therewith, it can be used in conjunction with HFCs to form blowing agent compositions that are more environmentally desirable and cheaper than compositions comprising HFCs alone.
Unfortunately, while water is highly beneficial for use in blowing agents from both environmental and cost standpoints, applicants have recognized several disadvantages associated with the use of water which counter these benefits. For example, one disadvantage associated with the use of water is that blowing agents containing water tend to produce foams having poorer thermal properties, including poorer thermal insulation, than water-free blowing agents. (See, for example, Sato H., et al., xe2x80x9cNovel Polyols for All Water-Blown and HCFC-141b Blown Rigid Polyurethane Foamsxe2x80x9d, Chemical Divisional R and D Report, Published Polyurethanes Expo""99 International Technical Conference and Exposition, 9/12-15, 1999; and U.S. Pat. No. 5,296,516 (issued to BASF Corp.), incorporated herein by reference). As noted above, water tends to aid in the blowing of foams by producing carbon dioxide. However, carbon dioxide tends to be a very poor insulating gas, having both a poor vapor thermal conductivity and a very quick diffusion rate. For this reason, foams blown with carbon dioxide tend to have poorer thermal characteristics, including poorer thermal insulation, than foams blown with hydrofluorocarbons alone.
In fact, as will be recognized by those of skill in the art, the thermal insulation characteristics of a foam is expected to worsen significantly as the amount of water in the composition used to blow the foam increases (more carbon dioxide is encapsulated in the foam and thus the foam tends to have more of the poor characteristics associated with carbon dioxide). Accordingly, it is often desirable to minimize the amount of water used in blowing agents to avoid such poor foam characteristics.
Another disadvantage associated with the use of water in blowing agents is that foams produced using water-containing blowing agents tend to degrade faster as the amount of water in the blowing agent is increased. As is known in the art, gasses encapsulated in closed-cell foams tend to diffuse out of the foams over time, resulting in undesirable xe2x80x9cagingxe2x80x9d of the foam. As used herein the term xe2x80x9cagingxe2x80x9d refers generally to the physical degradation of a foam and/or a decrease in the thermal insulation associated with a foam. Applicants have determined that carbon dioxide tends to diffuse out of blown foams faster (has a higher diffusion coefficient) than fluorocarbon gasses. Accordingly, foams containing a higher percentage of carbon dioxide (blown with a higher amount of water) tend to diffuse out a higher amount of the gas over time and therefore age faster than foams containing lower levels of carbon dioxide.
Applicants have thus recognized the need for environmentally-desirable and cost-effective compositions that can be used as blowing agents to produce foams having good thermal properties. In particular, applicants have identified a need for compositions containing HFCs and water that produce foams having desirable characteristics, including good thermal insulation and good xe2x80x9cagingxe2x80x9d characteristics, that are not impaired significantly despite relatively significant changes in the amount of water therein. Unfortunately, such compositions are not only uncommon, but also unpredictable.